AlGaAs Photovoltaics for Indoor Energy Harvesting in mm-Scale Wireless Sensor Nodes

Indoor photovoltaic energy harvesting is a promising candidate to power millimeter (mm)-scale systems. The theoretical efficiency and electrical performance of photovoltaics under typical indoor lighting conditions are analyzed. Commercial crystalline Si and fabricated GaAs and Al
_0.2
Ga
_0.8
As photovoltaic cells were experimentally measured under simulated AM 1.5 solar irradiation and indoor illumination conditions using a white phosphor light-emitting diode to study the effects of input spectra and illuminance on performance. The Al
_0.2
Ga
_0.8
As cells demonstrated the highest performance with a power conversion efficiency of 21%, with open-circuit voltages >0.65 V under low lighting conditions. The GaAs and Al
_0.2
Ga
_0.8
As cells each provide a power density of ~100 nW/mm
²
or more at 250 lx, sufficient for the perpetual operation of present-day low-power mm-scale wireless sensor nodes.